Hydrogenation of aldehyde or ketone compounds with Fe/tridentate ligands complexes

ABSTRACT

The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of Fe complexes with tridentate ligands, having one amino or imino coordinating group and two phosphino coordinating groups, in hydrogenation processes for the reduction of ketones or aldehydes, into the corresponding alcohol or diol, respectively.

RELATED APPLICATIONS

This application is a 371 filing of International Patent Application PCT/EP2016/063893 filed 16 Jun. 2016, which claims the benefit of European patent application no 15172581.9 filed 17 Jun. 2015. The contents of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of Fe complexes with tridentate ligands, in hydrogenation processes for the reduction of ketones or aldehydes into the corresponding alcohol or diol, respectively.

PRIOR ART

Reduction of ketone or aldehyde to the corresponding alcohol is one of the fundamental reactions in organic chemistry, and is used in a large number of chemical processes. In general, two main types of processes are known to achieve such a transformation. Such types of processes are the following:

a) hydride processes, in which a silyl or metal hydride salt, such as LiAlH₄, is used;

b) hydrogenation processes, in which molecular hydrogen is used.

From a practical point of view, hydrogenation processes are more attractive as they can be run using small amounts of catalyst (typically 10 to 1000 ppm relative to the substrate) and in the presence of small quantities or even in the absence of solvent. Furthermore, hydrogenation processes do not require the use of highly reactive and expensive hydrides, and do not produce important amounts of aqueous waste.

One of the mandatory and characterizing elements of hydrogenation processes is the catalyst or the catalytic system which is used to activate the molecular hydrogen in view of the reduction. The development of useful catalysts or catalytic systems for the hydrogenation of a carbonyl functional group represents still an important need in chemistry.

Amongst the few catalysts or catalytic systems known to perform such reductions one may cite the ruthenium/amino-phosphine complexes, extensively reported in the literature (e.g. Noyori, R Angew. Chem. Int. Ed. 2001, 40, 40-73; Saudan, L. A. in Dunn, P. J.; Hii, K. K.; Krische, M. J.; Williams M. T. Editors. Sustainable Catalysis, J. Wiley & Sons, New Jersey; 2013, pp 37-61). However, such systems, although being highly performing, suffer from requiring highly expensive and toxic ruthenium metal.

Morris (see Inorg. Chem. 2010, 49, 1094) reported two Iron complexes with a PNP-pincer imine ligand having acetonitrile as ligand, and wherein no activity or use is reported or suggested. More recently, Morris (J. Am. Chem. Soc., 2014, 136(22), 1367) disclosed the fine-tuning of the complex here-above by replacing the acetonitrile ligand by carbon monoxide and the use of this one as a catalyst for hydrogenation of ketone. However, this catalyst requires a preactivation with LiAlH₄ and are inefficient toward the reduction of α,β-unsaturated ketone.

Milstein (see Angew. Chem. Int. Ed, 2011, 50, 2120) reported an aldehyde, ketone hydrogenation using an iron complex with a tridentate pyridine derivative. The document shows weak selectivity on enones/enals as well as moderate activity toward if) standard aldehyde, ketone.

The hydrogenations described in these prior arts are always carried out in a presence of a base which represents a drawback for certain substrates leading, in such conditions, to formation of polymer instead of the alcohol product.

So there is a need for base-free hydrogenation process. One solution was proposed by Milstein (see Chem. Eur. J., 2012, 18, 7196). Indeed, the use of [(i-Pr—PNP)Fe(CO)(HBH₄)] as catalyst, wherein the PNP ligand is a tridentate pyridine derivative, allows avoiding the addition of a base to activate the catalyst toward hydrogenation. Nevertheless, these base-free conditions have not improved the selectivity issue on enones/enals and the activity toward standard ketone. Furthermore the addition of base is needed in order to hydrogenate aldehydes.

Therefore, there is a need for hydrogenation processes using catalysts or pre-catalysts with an alternative activation mode free of base and presenting a broader spectrum of substrates and if possible with enhanced selectivity.

DESCRIPTION OF THE INVENTION

In order to overcome the problems aforementioned, the present invention relates to processes for the reduction by hydrogenation, using molecular H₂, of a C₃-C₇₀ substrate containing one or two ketones or aldehydes into the corresponding alcohol, or diol, characterized in that said process is carried out in the presence of at least one catalyst in the form of a iron complex of a tridentate ligand wherein the coordinating groups consist of one amino or imino group and two phosphino group and optionally a salt of formula MX wherein M is an alkali metal cation and X a non-coordinating mono anion.

By the expression “in the presence of at least one catalyst . . . and optionally a salt of formula MX . . . ” or the similar, it is meant that the reaction can be carried out in present of catalyst or in presence of catalyst and MX.

According to an embodiment of the invention, said amino group is a secondary (i.e. NH) amino group.

According to a particular embodiment of the invention, the substrate can be a compound of formula (I)

wherein R^(a) and R^(b), taken together, represent a C₃-C₂₀, preferably C₄-C₂₀, hydrocarbon group, optionally substituted and optionally comprising one, two or three oxygen or nitrogen atoms; or, when said R^(a) and R^(b) are taken separately, R^(a) represents a hydrogen atom or a R^(b) group; and R^(b) represents a C₁-C₃₀ hydrocarbon group, optionally substituted and optionally comprising one, two or three oxygen or nitrogen atoms.

The corresponding alcohol (i.e (II-a)), is of formula

wherein R^(a) and R^(b) are defined as in formula (I).

It is understood that by “ . . . hydrocarbon group . . . ” it is meant that said group can be in the form of a linear, branched or cyclic aromatic, alkyl, alkenyl, alkandienyl or alkynyl group, e.g., a cyclic alkyl group, or can also be in the form of a mixture of said type of groups, e.g. a specific group may comprise a linear alkyl, a branched alkandienyl (e.g. having one or more carbon-carbon double bonds), a (poly)cyclic alkyl and an aryl moiety, unless a specific limitation to only one type is mentioned. Similarly, in all the below embodiments of the invention, when a group is mentioned as being in the form of more than one type of topology (e.g. linear, cyclic or branched) and/or unsaturation (e.g. alkyl, aromatic or alkenyl), it is meant also a group which may comprise moieties having any one of said topologies or unsaturations, as explained above. Similarly, in all the below embodiments of the invention, when a group is mentioned as being in the form of one type of unsaturation, (e.g. alkyl), it is meant that said group can be in any type of topology (e.g. linear, cyclic or branched) or having several moieties with various topologies.

According to any one of the embodiments of the invention, said aldehyde or ketone is one that will provide an alcohol, or a diol, that is useful in the pharmaceutical, agrochemical or perfumery industry as final product or as an intermediate. Particularly preferred substrate is an aldehyde or ketone, which will provide an alcohol, or diol, which is useful in the perfumery industry as final product or as an intermediate.

According to any one of the embodiments of the invention, the substrate is a C₅-C₃₀ compound of formula (I), or even a C₅-C₂₀ compound of formula (I).

According to any one of the embodiments of the invention, one may cite as substrate the one wherein R^(a) represents a hydrogen atom or a R^(b) group, and each R^(b), when taken separately, represents simultaneously or independently a linear, branched or cyclic C₁-C₃₀ aromatic, alkyl, alkenyl or alkanedienyl group optionally substituted and optionally comprising one or two oxygen or nitrogen atoms; or R^(a) and R^(b) are bonded together and form a C₄-C₂₀ saturated or unsaturated linear, branched, mono-, di- or tri-cyclic group, optionally substituted and optionally comprising one or two oxygen or nitrogen atoms.

According to any one of the embodiments of the invention, one may cite as substrate those wherein R^(a) represents a hydrogen atom or a R^(b) group, and each R^(b), when taken separately, represent simultaneously or independently a linear, branched or cyclic C₃-C₁₈ aromatic, alkyl, alkenyl or alkanedienyl group optionally substituted; or R^(a) and R^(b) are bonded together and form a C₅-C₂₀ saturated or unsaturated linear, branched, mono-, di- or tri-cyclic group, optionally substituted.

According to any one of the above embodiments of the invention, when R^(b) is an alkenyl or alkadienyl group, then said group is an alk-1-enyl or an alka-1,3-dienyl group (i.e. the carbon carbon double bonds are conjugated with the carbonyl group).

According to a prefer embodiment R^(b) is a C₃₋₁₈ alk-1-enyl group wherein the carbon carbon double bond is di or tri substituted; i.e. compound of formula (I) is a α,β-unsaturated ketone or aldehyde also knowns as an enol or an enal. Even more preferably, R^(b) is an alk-1-enyl group wherein the carbon carbon double bond is di-substituted.

According to any one of the above embodiments of the invention, when R^(a) is a hydrogen atom, R^(b) may represent in particular a branched or cyclic hydrocarbon group wherein the branching is in the alpha position relative to the CHO group of the substrate.

Possible substituents of R^(a) and R^(b) are one, two or three halogen, OR^(c), NR^(c) ₂ or R^(c) groups, in which R^(c) is a hydrogen atom, a halogenated C₁-C₂ group or a C₁ to C₁₀ cyclic, linear or branched alkyl, or alkenyl group, preferably a C₁ to C₄ linear or branched alkyl or alkenyl group. As other possible substituents one may also cite a group COOR^(c), which can also be reduced to the corresponding alcohol during the invention's process, according to the molar amount of H₂ used, as well known by a person skilled in the art.

According to a particular aspect of the invention, the possible substituents of R^(a) and R^(b) are one or two halogen, OR^(c), NR^(c) ₂ or R^(c) groups, in which R^(c) is a hydrogen atom, a C₁ to C₆ cyclic, linear or branched alkyl, or alkenyl group, preferably a C₁ to C₄ linear or branched alkyl or alkenyl group.

Non-limiting examples of substrates of formula (I) are the following:

-   -   C₃₋₁₄ aldehydes such as:         a C₃₋₁₀ alkanal, a C₃₋₁₀ 2-alkenal, a C₃₋₁₀ 2-methyl-2-alkenal,         a C₅₋₁₀ 2,4-dienal, a 3-alkyl-3-benzene-prop-2-enal, a         3-alkyl-2-methyl-3-benzene-prop-2-enal, a         C₇₋₁₀-benzene-carbaldehyde, a C₅₋₁₀         cycloalk-1-ene-1-carbaldehyde, a C₄₋₁₂ 2-methylen-aldehyde;         wherein the underlined compounds are known to be particularly         base-sensitive substrates;     -   C₃₋₁₇ ketones such as:         a di(C₁₋₁₂ alkyl) ketone, a C₄-C₁₂ cyclic-ketone, a         cyclopentenone alpha substituted by a C₅₋₁₂ hydrocarbon group, a         cylohex-2-en-1-one substituted by zero to three methyl groups, a         cyclohexenone alpha substituted by a C₆₋₁₂ hydrocarbon group, a         substituted aryl C₁₋₁₂-alkyl ketone, a substituted aryl         C₂₋₁₂-1-alkene methyl ketone, a substituted cyclohexenyl         C₂₋₆-1-alkene methyl ketone, a C₂₋₁₂-1-alkene methyl ketone, a         C₂₋₁₅-2-alkene-1,1-dimethyl methyl ketone, a         C₂₋₁₅-2-alkyl-1,1-dimethyl methyl ketone; wherein the underlined         compounds are known to be particularly base-sensitive         substrates.

The process of the invention is characterized by the use, as catalyst or pre-catalyst (hereinafter referred to as complexes unless specified otherwise), of an iron complex as described above. The complex can be in the form of an ionic or neutral species.

According to an embodiment of the invention, the iron complex can be of the general formula [Fe(L3)(L′)(Y)(Z)]  (1) wherein L3 represents a tridentate ligand wherein the coordinating groups consist of one amino or imino group and two phosphino groups; L′ represents a CO or C₁₋₁₁ isonitrile compound; Y represents a hydrogen atom or a C₁-C₁₄ carboxylic radical; and Z represents a hydroxyl group, a C₁-C₁₄ carboxylic radical or a linear C₁-C₁₄ alkoxy radical.

By “C₁ to 14 carboxylic radical” or the similar, it is meant the normal meaning in the art, i.e. a RCOO radical wherein R group is a hydrogen atom or a C₁ to ₁₃ hydrocarbon group optionally comprising one or two oxygen or nitrogen atoms. Preferably R is an alkyl or aromatic group optionally substituted and optionally comprising one or two oxygen or nitrogen atoms.

The person skill in the art is well aware than Y and/or Z could be in the coordinative sphere of the Iron or could be decoordinated, in particular when Y and/or Z represent an alkoxy or carboxylic radical.

In a particular embodiment of the invention, said L3 ligand may be a C₆-C₄₀, or even a C₆-C₃₀, compound.

According to any embodiment of the invention, in formula (1), Y may represent a hydrogen atom, or a C₁ to C₈ carboxylic radical such as a HCOO, CH₃COO or CH₃CH₂COO radical. More preferably, Y may represent a hydrogen atom,

According to any embodiment of the invention, in formula (1), Z may represent, hydroxy radical.

According to any embodiment of the invention, in formula (1), Z may represent a C₁-C₁₄ carboxylic radical optionally substituted by one to three ether functional groups. Preferably, Z may represent a C₁ to C₈ alkyl carboxylic radical such as a HCOO, CH₃COO or CH₃CH₂COO radical optionally substituted by one to three ether functional groups or a C₇ to C₁₃ aromatic carboxylic radical optionally substituted by one to three alkyl or ether groups such as 4-phenylbenzoicCOO, 3,5-dimethylphenylCOO or p-MeOphenylCOO. More preferably, Z may represent a C₁ to C₆ alkyl carboxylic radical or a C₈ to C₁₃ aromatic carboxylic radical optionally substituted by an alkyl or ether groups. More preferably, Z may represent a C₁ to C₅ alkyl carboxylic radical or a C₈ to C₉ aromatic carboxylic radical wherein the aromatic ring is preferably substituted by an electron donating group such as a methyl or a methoxy group. More preferably, Z may represent, a C₁ to C₄ alkyl carboxylic radical. Even more preferably, Z may represent a formate, an acetate or a pivalate radical. Even more preferably, Z may represent a formate or an acetate radical. Said complex, wherein Z represents a formate has been only reported in Lewis acid-assisted formic acid dehydrogenation reaction (J. Am. Chem. Soc. 2014, 136, 10234-10237).

According to another embodiment, Z may represent an acetate or a pivalate radical.

According to any embodiment of the invention, in formula (1), Z may represent a linear C₁-C₁₄ alkoxy. Preferably, Z may represent, a linear C₁ to C₆ alkoxy radical, such as a methoxy, ethoxy, propoxy or butoxy radical. More preferably, Z may represent a linear C₁ to C₄ alkoxy radical. More preferably, Z may represent a methoxy or ethoxy radical, preferably a methoxy radical.

By the term “an electron donating group” or the similar, it is meant the normal meaning in the art, i.e. an atom or functional group capable of donating some of its electronic density to the adjacent aromatic system, e.g. alkoxy, alkyl or amine group.

According to any embodiment of the invention, L′ may represent a CO.

According to any one of the above-mentioned embodiments, the tridentate ligand L3 can be a compound of one of the formula

wherein the dotted line indicates a single or double bond; z is 0 or 1 when the carbon-nitrogen bond with the dotted line represents a double or single bond respectively; R¹ and R², when taken separately, represent, simultaneously or independently, a linear, branched or cyclic C₁ to C₁₀ alkyl or alkenyl group optionally substituted, a C₆ to C₁₀ aromatic group optionally substituted; said groups R¹ and R², when taken together, may form a saturated or unsaturated ring optionally substituted, having 5 to 10 atoms and including the phosphorus atom to which said R¹ and R² groups are bonded; R⁶ and R⁷ represent, simultaneously or independently, a hydrogen atom, a linear, branched or cyclic C₁ to C₆ alkyl or alkenyl group optionally substituted, a C₆-C₁₀ aromatic group optionally substituted; when the dotted line represent a single bond, two R⁶ taken together, may form a saturated heterocycle, optionally substituted and optionally containing one or two additional nitrogen or oxygen atoms, containing 5 to 10 atoms and including the N atom and the carbon atoms to which said R⁶ groups are bonded respectively; and Q represents:

-   -   a group of formula

wherein n is an integer from 1 to 3, and

-   -   R⁴ and R⁵ represent, simultaneously or independently, a hydrogen         atom, a linear, branched or cyclic C₁ to C₆ alkyl or alkenyl         group optionally substituted, a C₆-C₁₀ aromatic group optionally         substituted; two distinct R⁴ and/or R⁵ groups, taken together,         may form a C₅ to C₈, saturated ring optionally substituted,         including the carbon atoms to which each of said R⁴ or R⁵ group         is bonded; or     -   a diphenyl, dinaphthyl, C₅-C₁₂ metallocediyl, phenylene or         naphthylene group optionally substituted.

According to any embodiment of the invention, by “aromatic group or ring” it is meant a phenyl or naphthyl derivative.

For the sake of clarity, by the expression “wherein one dotted line represents a single or double bond”, or the similar, it is meant the normal meaning understood by a person skilled in the art, i.e. that the whole bonding (solid and dotted line) between the carbon and nitrogen atoms connected by said dotted line, is a carbon-nitrogen single or double bond.

According to any one of the above-mentioned embodiments, the tridentate ligand L3 can be a compound of one of the formula

wherein the R¹, R², R⁶ and R⁷ have the meaning indicates in formula (A).

According to any embodiment of the invention, R¹ and R², when taken separately, represent, simultaneously or independently, a linear, branched or cyclic C₁ to C₁₀ alkyl group optionally substituted, a C₆-C₁₀ phenyl or naphthyl group optionally substituted; said groups R¹ and R², when taken together, may form a saturated ring optionally substituted, having 5 to 10 atoms and including the phosphorus atom to which said R¹ and R² groups are bonded.

According to any embodiment of the invention, R¹ and R² are taken separately and each represent, simultaneously or independently, a linear, branched or cyclic C₁, or even C₃, to C₆ alkyl group optionally substituted, a phenyl group optionally substituted.

According to any embodiment of the invention, R⁶ and R⁷ represent, simultaneously or independently, a hydrogen atom, a linear, branched or cyclic C₁ to C₆ alkyl group optionally substituted, a phenyl group optionally substituted; when the dotted line represent a single bond, two R⁶ taken together, may form a saturated heterocycle, optionally substituted and optionally containing one additional nitrogen or oxygen atoms, containing 5 or 6 atoms and including the N atom and the carbon atoms to which said R⁶ groups are bonded respectively.

According to any embodiment of the invention, one or two R⁷ are hydrogen atoms. Similarly one or two R⁶ are hydrogen atoms.

According to any embodiment of the invention, Q represents:

-   -   a group of formula

wherein n is 1 or 2, and

-   -   R⁴ and R⁵ represent, simultaneously or independently, a hydrogen         atom, a linear, branched or cyclic C₁ to C₆ alkyl group         optionally substituted, a C₆-C₁₀ phenyl or naphthyl group         optionally substituted; or     -   a C₅-C₁₂ ferrocenediyl, 1,2-phenylene or 1,2- or 2,3-naphthylene         group optionally substituted.

According to any embodiment of the invention, Q represents a group of formula (i)

wherein n is 1 or 2, and R⁴ and R⁵ represent, simultaneously or independently, a hydrogen atom, a linear, branched or cyclic C₁ to C₆ alkyl group optionally substituted, a phenyl group optionally substituted.

According to any embodiment of the invention, Q represents a linear methylene or ethylene group optionally substituted.

According to any embodiment of the invention, possible substituents of R⁴, R⁵, R⁶ and R⁷ are one or two halogen, C₁ to C₁₀ alkoxy groups, halo- or perhalo-hydrocarbon, COOR, NR₂, quaternary amine or R groups, wherein R is a C₁ to C₆ alkyl, or a C₅ to C₁₂ cycloalkyl, aralkyl (such as benzyl, phenethyl etc.) or aromatic group, the latter being also optionally substituted by one, two or three halogen, sulfonates groups or C₁-C₈ alkyl, alkoxy, amino, nitro, sulfonates, halo- or perhalo-hydrocarbon or ester groups. By “halo- or perhalo-hydrocarbon” it is meant groups such as CF₃ or CClH₂ for instance.

According to any embodiment of the invention, possible substituents of R⁴, R⁵, R⁶ and R⁷ are one or two halogen, C₁ to C₆ alkoxy groups, COOR, NR₂, quaternary amine or R groups, wherein R is a C₁ to C₆ alkyl, or a C₅ to C₁₂ cycloalkyl, aralkyl (such as benzyl, phenethyl etc.) or aromatic group, the latter being also optionally substituted by one, two or three halogen, sulfonates groups or C₁-C₈ alkyl, alkoxy, amino, nitro, sulfonates, halo- or perhalo-hydrocarbon or ester groups.

Possible substituents of R¹ and R³ and Q, in particular when said groups are or contain phenyl or aromatic groups or moieties, one to three C₁ to C₅ alkoxy groups, C₁ to C₄ alkyl groups, or NR groups, wherein R is a C₁ to C₆ alkyl C₅ to C₆ cycloalkyl.

The processes of the invention are particularly attractive when L3 represents a ligand of the formula (C):

wherein Alk is a C₃₋₁₀, or even C₃₋₆, branched or cyclic alkyl group. Preferably Alk may represent an isopropyl group.

According to any embodiment of the invention, the process of the invention is performed in absence of base.

Certain complexes according to the invention are also new. Therefore, another object of the present invention is a complex of formula [Fe(L3)(L′)(Y)(Z)]  (1) wherein L3, L′ and Y have the same meaning as above; and Z represents a C₂ to C₆ alkyl carboxylic radical or a C₇ to C₁₄ aromatic carboxylic radical; i.e. Z does not represent a formate.

The ligands described above can be obtained by applying standard general methods which are well known in the state of the art and by the person skilled in the art. Therefore, their preparation does not require a specific description. For example one may revert to Edwards, P. G. Polyhedron 1990, 9, 2413-2418.

In a general way, the complexes of formula (1) or (2) can be prepared and isolated prior to their use in the process according to the general methods described in the literature. A method is described in the Example.

Moreover, the complexes can be prepared in situ, by several methods, without isolation or purification, just before their use as described in the Example or also one may use as starting complexes the ones of formula [Fe(L3′)(L′)Y]  (3)

-   -   wherein L3′ represents a L3 with deprotonated amine; i.e. L3′ is         an amido ligand, and L′ and Y are as defined above;         which are then reacted with a C₁-C₁₄ carboxylic acid.

A salt of formula MX wherein M is an alkali metal cation and X a non-coordinating mono anion can be optionally added in order to carry out the process of the present invention.

According to any one of the above embodiments, M represents an alkali metal cation such as Na, K, Cs or Li and X represents a non-coordinative anion such as BF₄ ⁻, CF₃SO₃ ⁻, PO₄ ³⁻, F⁻, PF₆ ⁻, BAr^(F) ₄ ⁻, Cl⁻ or CF₃COO⁻.

According to a particular embodiment, MX may be selected from the group consisted of NaBF₄, KBF₄, CsBF₄, LiF and K₃PO₄. Preferably MX is NaBF₄, KBF₄ or CsBF₄, even more preferably MX is KBF₄.

According to a prefer embodiment, the process of the invention is carried out in presence of a salt of formula MX.

As previously mentioned the processes of the invention consist in the hydrogenation of a substrate using an iron complex and optionally MX. A typical process implies the mixture of the substrate with the iron complex and optionally MX and a solvent, and then treating such a mixture with molecular hydrogen at a chosen pressure and temperature.

The complexes of the invention, an essential parameter of the process, can be added to the reaction medium in a large range of concentrations. As non-limiting examples, one can cite as complex concentration values those ranging from 50 ppm to 50000 ppm, relative to the amount of substrate. Preferably, the complex concentration will be comprised between 100 and 20000 ppm, or even between 1000 and 10000 ppm. It goes without saying that the optimum concentration of complex will depend, as the person skilled in the art knows, on the nature of the latter, on the nature of the substrate and on the pressure of H₂ used during the process, as well as the desired time of reaction.

Useful quantities of MX, added to the reaction mixture, may be comprised in a relatively large range. One can cite, as non-limiting examples, ranges between 0.0005 to 0.2 molar equivalents, relative to the substrate, preferably 0.001 to 0.10, and even more preferably between 0.05 to 0.10 molar equivalents.

The hydrogenation reaction can be carried out in the presence or absence of a solvent. When a solvent is required or used for practical reasons, then any solvent current in hydrogenation reactions can be used for the purposes of the invention. Non-limiting examples include aromatic solvents such as toluene or xylene, hydrocarbon solvents such as hexane, heptane or cyclohexane, ethers such as tetrahydrofuran or MTBE, polar solvents such as primary or secondary alcohols such as isopropanol or ethanol, or mixtures thereof. Preferably, the solvent is selected from the group consisting of THF, toluene and heptane. The choice of the solvent is a function of the nature of the complex and the person skilled in the art is well able to select the solvent most convenient in each case to optimize the hydrogenation reaction.

In the hydrogenation process of the invention, the reaction can be carried out at a H₂ pressure comprised between 10⁵ Pa and 80×10⁵ Pa (1 to 80 bar) or even more if desired. Again, a person skilled in the art is well able to adjust the pressure as a function of the catalyst load and of the dilution of the substrate in the solvent. As examples, one can cite typical pressures of 1 to 50×10⁵ Pa (1 to 50 bar).

According to a particular embodiment of the invention, the atmosphere of the reaction medium may also contain about 0.001 and 0.10%, or even 0.01 and 0.05%, of CO relative to the molar amount of H₂.

The temperature at which the hydrogenation can be carried out is comprised between 0° C. and 120° C., more preferably in the range of between 20° C. and 100° C., or even between 50° C. and 100° C. Of course, a person skilled in the art is also able to select the preferred temperature as a function of the presence of MX, of the melting and boiling point of the starting and final products as well as the desired time of reaction or conversion.

The invention will now be described in further detail by way of the following examples, wherein the temperatures are indicated in degrees centigrade and the abbreviations have the usual meaning in the art.

All the procedures described hereafter have been carried out under an inert atmosphere unless stated otherwise. Hydrogenations were carried out either in open glass tubes placed inside a stainless steel autoclave or directly in the autoclave. H₂ gas (99.99990%) was used as received. All substrates and solvents were distilled from appropriate drying agents under Ar. NMR spectra were recorded on a Bruker AM-400 (¹H at 400.1 MHz, ¹³C at 100.6 MHz, and ³¹P at 161.9 MHz) spectrometer and normally measured at 300 K, in CD₂Cl₂ unless indicated otherwise. Chemical shifts are listed in ppm downfield from tetramethylsilane. ³¹P NMR chemical shifts are reported in ppm downfield from H₃PO₄ and referenced to an external 85% solution of phosphoric acid in D₂O as standard.

EXAMPLES Example 1 Preparation of carbonyl dibromo bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(Cl₂)

(prepared according to: I. Koehne, T. J. Schmeier, E. A. Bielinski, C. J. Pan, P. O. Lagaditis, W. H. Bernskoetter, M. K. Takase, C. Würtele, N. Hazari, S. Schneider, Inorg. Chem. 2014, 53, 2133-2143):

Under an argon atmosphere, to a stirred suspension of iron(II) chloride (620 mg, 4.89 mmol) in THF (21 mL) in a heavy wall glass tube was added bis(2-(diisopropylphosphino)ethyl)amine, L-1, (prepared according to A. A. Danopoulos, A. R. Wills, P. G. Edwards, Polyhedron 1990 9, 2413-2418) (1.5 g, 4.91 mmol) at 25° C. More THF (3×1 mL) was added to rinse. The milky white solution was heated at 65° C. during 1 h. After cooling to room temperature, the suspension was placed under CO atmosphere (2 bar), after purging with CO (3×1 bar). The mixture was stirred under CO atmosphere overnight. After 10 min, a deep purple solution was obtained with total dissolution of the solid. Evaporation of the solvent under vacuum afforded a deep purple solid which was dissolved in DCM (10 mL) and added drop wise to pentane (50 mL). The suspension was concentrated following by addition of more pentane (10 mL), and concentrated until the supernatant became clear. The purple solid was filtrated, washed with pentane (2×5 mL) and finally dried under vacuum (0.1 mbar/1 h). The desired complex was obtained as a deep purple solid (2.133 gr, 95% yield).

Example 2 Preparation of carbonyl hydridobromo bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(H)(Cl))

(prepared according to: a) I. Koehne, T. J. Schmeier, E. A. Bielinski, C. J. Pan, P. O. Lagaditis, W. H. Bernskoetter, M. K. Takase, C. Würtele, N. Hazari, S. Schneider, Inorg. Chem. 2014, 53, 2133-2143; b) S. Chakraborty, H. Dai, P. Bhattacharya, N. T. Fairweather, M. S. Gibson, J. A. Krause, H. Guan, J. Am. Chem. Soc. 2014, 136, 7869-7872):

Under an argon atmosphere, a 50 mL oven-dried Schlenk flask equipped with a stirring bar was charged with (Fe(L-1)(CO)Cl₂) (500 mg, 1.087 mmol) and NaBH₄ (44.5 mg, 1.176 mmol). Adding EtOH (40 mL) to this mixture at 0° C., resulted in a yellow solution in few minutes. The resulting mixture was gradually warmed to room temperature and then stirred for additional 16 h. Removal of the volatiles under vacuum afforded an orange brown solid, which was treated with toluene (30 mL) and then filtered through a pad of Celite to give an orange solution. Evaporating the solvent under vacuum yielded the desired compound as a bright orange powder (419 mg, 91% yield).

Example 3 Preparation of carbonyl Amido bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(H))

(prepared according to: E. A. Bielinski, P. O. Lagaditis, Y. Zhang, B. Q. Mercado, C. Würtele, W. H. Bernskoetter, N. Hazari, S. Schneider, J. Am. Chem. Soc. 2014, 136, 10234-10237):

Under an argon atmosphere, a schlenk was charged with (Fe(L-1)(CO)(H)Cl (340 mg, 0.8 mmol) and KO^(t)Bu (98 mg, 0.87 mmol). Upon addition of THF (20 mL) at room temperature an immediate colour change from yellow to red-purple was observed. The suspension was stirred for 30 minutes at room temperature and the solvent was evaporated in vacuum. The red-purple residue was extracted with pentane, filtered over Celite and then the solvent was removed. The desired red-purple complex was dried under vacuum (0.1 mbar, 1 h) to give a dark-purple solid (305 mg, 98% yield).

Example 4 Preparation of carbonyl hydridoformate bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(H)(OC(O)H)) (C1)

(prepared according to: E. A. Bielinski, P. O. Lagaditis, Y. Zhang, B. Q. Mercado, C. Würtele, W. H. Bernskoetter, N. Hazari, S. Schneider, J. Am. Chem. Soc. 2014, 136, 10234-10237.):

Under an argon atmosphere, a solution of formic acid (30 mg, 0.65 mmol) in THF (2 mL) was added to Fe(L-1)(CO)H (250 mg, 0,642 mmol) in THF (3 mL) at room temperature. The magenta mixture changed directly to a green-yellow solution. The mixture was stirred for 10 min at room temperature after which the solvent was evaporated and the residue was dissolved in pentane filtered and the solvent evaporated to give a yellow brown oily solid. The crude was triturated with pentane cooled to −20° C. then after removing of the solvent a yellow solid was obtained (220 mg, 79% yield).

Example 5 Preparation of carbonyl hydridopivalate bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(H)(OC(O)^(t)Bu)) (C2)

Under an argon atmosphere, a solution of pivalic acid (2.1 ml at 0.11M, 0.23 mmol) in THF was added to Fe(L-1)(CO)H (93 mg, 0.239 mmol) in THF (3 mL) at room temperature. The magenta mixture changed directly to a green-yellow solution. The solution was stirred for 10 min at room temperature after which the solvent was evaporated and the residue was dissolved in pentane filtered and the solvent evaporated to give an orange-yellow solid (117 mg, >99% yield).

¹H-NMR (C₆D₆, 500 MHz) δ: 9.56 (bs, 1H), 2.85-2.7 (m, 2H), 2.74-2.86 (m, 2H), 1.97-2.05 (m, 2H), 1.71-1.83 (m, 4H), 1.63 (dd, 7.5, 15 Hz, 8H), 1.35 (s, 9H), 1.21 (dd, 7.2, 14.8 Hz, 6H), 1.12 (dd, 5.9, 11 Hz, 6H), 0.88 (dd, 6.8, 13 Hz, 6H), −25.7 (t, 50.6 Hz, 1H).

¹³C-NMR (C₆D₆, 100 MHz) δ: 189.91 (s, C, OC(O)), 53.7 (t, CH₂, JCP=6.2 Hz, NHCH₂), 40.8 (s, C, C(CH₃)₃), 29.8 (t, CH₂, JCP=7.1 Hz, NHCH₂P), 28.9 (s, CH₃, C(CH₃)₃), 28.0 (t, CH, JCP=7.9 Hz, PCH(CH₃)₂), 25.3 (t, 2C, JCP=12.6 Hz, PCH(CH₃)₂), 21.4 (t, CH₃, JCP=2.3 Hz), 20.4 (t, CH₃, JCP=2.3 Hz), 19.2 (s, CH₃), 17.8 (t, CH₃, JCP=2.3 Hz) CO resonance not detected.

³¹P {¹H}-NMR (C₆D₆, 200 MHz): 96.7 (d, JPH=23.59 Hz).

Example 6 Preparation of carbonyl hydridoacetate bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(H)(OC(O)Me)) (C3)

Under an argon atmosphere, a solution of acetic acid (2.1 ml at 0.11M, 0.23 mmol) in THF was added to Fe(L-1)(CO)H (90.6 mg, 0.23 mmol) in THF (3 mL) at room temperature. The magenta mixture changed directly to a green-yellow solution. The solution was stirred for 10 min at room temperature after which the solvent was evaporated and the residue was dissolved in pentane filtered and the solvent evaporated to give an orange-yellow solid (102 mg, 98% yield).

¹H-NMR (C₆D₆, 500 MHz) δ: 9.44 (bs, 1H), 2.88-2.71 (m, 2H), 2.19-2.16 (m, 2H), 2.09 (s, 3H), 1.97-1.93 (m, 2H), 1.87-1.81 (m, 2H), 1.78-1.70 (m, 2H), 1.66-1.62 (m, 2H), 1.55 (q, J=7.3 Hz, 6H), 1.22-1.16 (m, 12H), 0.91 (dd, 6.8, 13.6 Hz, 6H), −25.7 (t, 50.2 Hz, 1H).

¹³C-NMR (C₆D₆, 100 MHz) δ: 183.0 (s, C, OC(O)), 53.6 (t, CH₂, JCP=6.13 Hz, NHCH₂), 29.3 (t, CH₂, JCP=6.92 Hz, NHCH₂P), 28.2 (t, CH, JCP=8 Hz, PCH(CH₃)₂), 26.5 (s, CH₃), 26.0 (t, 2C, JCP=12.7 Hz, PCH(CH₃)₂), 20.4 (s, CH₃), 20.0 (s, CH₃), 19.1 (s, CH₃), 18.2 (s, CH₃), CO resonance not detected.

³¹P{¹H}-NMR (C₆D₆, 200 MHz): 95.78 (d, JPH=19.9 Hz, 98%), 52.2 (s, Free oxidized ligand, 0.8%), −2.04 (s, free ligand)

Example 7 Catalytic Hydrogenation of Acetophenone Using Complexes Fe(L-1)(CO)(H)(OC(O)R)

A typical experimental procedure is as follows:

In a glow box under argon, test tubes were charged successively with the desired complexes Fe(L-1)(CO)(H)(OC(O)R) (0.25-0.5 mol %) and with KBF₄ (5-10 mol %) or without any additive. Then a solution of acetophenone (3 mmol) dissolved in THF (2 mL) was added. The tubes were then placed in a parallel hydrogenation apparatus and heated to the corresponding temperature, then pressurised with hydrogen gas at 20 bar and mechanically stirred. After 8 h, the parallel hydrogenation apparatus was cooled to room temperature, depressurized, and each tube analysed by GC (DB-Wax).

Under these conditions several complexes Fe(L-1)(CO)(H)(OC(O)R) as reported in Table 1 were tested. The results are reported in Table 2.

TABLE 1 Structures and names of complexes Fe(L-1)(CO)(H)(OC(O)R) used Com- plexes Structure Name C1

Carbonyl hydrido formate bis[2-(di- isopropylphosphino) ethyl] amine iron (II) Fe(L-1)(CO)(H)(OC(O)H) C2

Carbonyl hydrido pivalate bis[2-(di- isopropylphosphino) ethyl] amine iron (II) Fe(L-1)(CO)(H)(OC(O)^(t)Bu) C3

Carbonyl hydrido acetate bis[2-(di- isopropylphosphino) ethyl] amine iron (II) Fe(L-1)(CO)(H)(OC(O)Me) C4

Carbonyl hydrido formate bis[2-(di- ethylphosphino) ethyl] amine iron (II) Fe(L-2)(CO)(H)(OC(O)H)

TABLE 2 Hydrogenation of acetophenone using isolated complexes Fe(L- 1)(CO)(H)(OC(O)R) Test Complexes C/MX2 T (° C.) Conv. ROH 1 C1 5000/0 50 73 73 2 C1 5000/0 100 >99 99.9 3 C1 5000/100000 50 >99 >99 4 C1 2500/100000 50 >99 >99 5 C1 2500/5000 50 90 90 6 C1 2500/0 50 67 67 7 C2 5000/0 100 89 89 8 C2 2500/100000 100 85 85 9 C2 2500/50000 100 85 85 10 C2 2500/0 100 60 60 11 C3 5000/100000 100 >99 99 12 C4 2500/100000 50 56 56 13 C4 2500/0 50 23 23 C/MX2: Catalyst/KBF₄ ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of acetophenone to 1-phenyl ethanol after 8 hours. Reaction conditions: H₂ gas (20 bar), 50° C. or 100° C., THF (1.5M). ROH: amount of 1-phenyl ethanol in percent in the reaction mixture as analysed by GC

Example 8 Catalytic Hydrogenation of Acetophenone Using Complexes Fe(L-1)(CO)(H)(OC(O)R) Generated In-Situ

A typical experimental procedure is as follows:

Solutions Stock:

-   -   A solution of carboxylic acid 0.11M in THF.     -   A solution of complex Fe(L-1)(CO)H 0.018M in THF.     -   A solution of 3M of acetophenone in THF.

In 1 ml solution of Fe(L-1-H)(CO)(H) (0.018 M) was added 0.2 mL of the carboxylic acid solution (0.11 M). A solution of Fe(L-1)(CO)(H)(carboxylic acid) of 0.015 M was obtained after 15 min of stirring.

In a glow box under argon, test tubes were charged with KBF₄ (10 mol %) or without. Then acetophenone (1 ml at 3M, 3.0 mmol) was added following by Fe(L-1)(CO)(H)(OC(O)R) (1 mL at 0.015M, 0.015 mmol). The tubes were then placed in a parallel hydrogenation apparatus and heated to the corresponding temperature, then pressurised with hydrogen gas at 20 bar and mechanically stirred. After 8 h, the parallel hydrogenation apparatus was cooled to room temperature, depressurized, and each tube analysed by GC (DB-Wax).

Under these conditions several complexes Fe(L-1)(CO)(H)(OC(O)R) as reported in Table 3 were tested. The results are reported in Table 4.

TABLE 3 Structure and names of carboxylic acids used with carbonyl amido bis[2-(di-isopropylphosphino)ethyl] amine iron (II) complex (Fe(L-1-H)(CO)(H)) to generate in situ the complex Fe(L-1)(CO)(H)(OC(O)R). Carboxylic Acid Structure Name CA1

Formic acid CA2

Acetic acid CA3

Pivalic acid CA4

Cyclo- hexanecarboxylic acid CA5

Benzoic acid CA6

4-Methoxybenzoic acid CA7

4-phenylbenzoic acid CA8

3,5-dimethylbenzoic acid

TABLE 4 Hydrogenation of acetophenone using complexes Fe(L-1)(CO)(H)(OC(O)R) formed in situ from the corresponding carboxylic acid and the carbonyl amido bis[2-(di- isopropylphosphino)ethyl] amine iron (II), (Fe(L-1-H)(CO)(H)) complex. Carboxylic Test Acid C/MX2 T (° C.) Conv. ROH 1 CA1 5000/0 50 73 73 2 CA1 5000/100000 50 >99 >99 3 CA2 5000/0 100 91 91 4 CA2 5000/100000 100 >99 99 5 CA3 5000/0 80 39 39 6 CA3 5000/100000 100 85 85 7 CA4 5000/0 100 56 56 8 CA4 5000/100000 100 76 7676 9 CA5 5000/0 100 10 10 10 CA5 5000/100000 100 36 36 11 CA6 5000/0 100 39 39 12 CA6 5000/100000 100 94 94 13 CA7 5000/0 100 7 7 14 CA7 5000/100000 100 88 88 15 CA8 5000/0 100 21 21 16 CA8 5000/100000 100 >99 >99 C/MX2: Catalyst/KBF₄ ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of acetophenone to the corresponding 1-phenyl ethanol after 8 h. Reaction conditions: H₂ gas (20 bar), 50° C.-100° C., THF (1.5M). ROH: amount of 1-phenyl ethanol in percent in the reaction mixture as analysed by GC

Example 9 Catalytic Hydrogenation of Acetophenone Using Complexes Fe(L-1)(CO)(H)(OC(O)R) with Various Salts of Formula MX

Following, the typical procedure as described in Example 8. Under these conditions several salts of formula MX as reported in Table 5 were tested. The results are reported in Table 6.

TABLE 5 Structure and names of salts of formula MX used with carbonyl hydridoformate bis[2-(di-isopropylphosphino)ethyl] amine iron (II), (Fe(L-1)(CO)(H)(OC(O)H)) or with carbonyl hydridoacetate bis[2-(di- isopropylphosphino)ethyl] amine iron (II), (Fe(L-1)(CO)(H)(OC(O)Me)) (generated in situ). MX Structure Name MX1 NaBF₄ Sodium tetrafluoroborate MX2 KBF₄ Potassium tetrafluoroborate MX3 CsBF₄ Cesium tetrafluoroborate MX4 KOTf Potassium triflate MX5 KPF₆ Potassium hexafluorophosphate MX6 K₃PO₄ Potassium phosphate MX7 LiF Lithium fluoride

TABLE 6 Hydrogenation of acetophenone using complexes Fe(L- 1)(CO)(H)(OC(O)R) formed in situ from the corresponding carboxylic acid and the carbonyl amido bis[2-(di- isopropylphosphino)ethyl] amine iron (II), (Fe(L- 1-H)(CO)H) complex with the corresponding MX. Com- T Test MX plexes C/MX (° C.) Conv. ROH 1 — C1 5000/0    50 73 73 2 MX1 C1 5000/100000 50 >99 >99 3 MX2 C1 5000/100000 50 >99 >99 4 MX2 C1 2500/50000  50 76 76 5 MX3 C1 5000/100000 50 >99 >99 6 MX4 C1 2500/50000  50 24 24 7 MX5 C1 2500/50000  50 13 13 8 MX6 C1 5000/100000 50 >99 >99 9 MX7 C1 5000/100000 50 92 91 10 MX2 C2 5000/100000 100 85 85 11 — C3 5000/100000 80 24 24 12 — C3 5000/100000 100 91 91 13 MX2 C3 5000/100000 100 99 99 C/MX: Catalyst/MX ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of acetophenone to the corresponding 1-phenyl ethanol after 8 h. Reaction conditions: H₂ gas (20 bar), 50° C.-100° C., THF (1.5M). ROH: amount of 1-phenyl ethanol in percent in the reaction mixture as analysed by GC

Example 10 Catalytic Hydrogenation of Acetophenone Using Complexes Fe(L-1)(CO)(H)(OC(O)R) with Different Solvents

A typical experimental procedure is as follows:

In a glow box under argon, test tubes were charged successively with Fe(L-1)(CO)(H)(OC(O)R) (0.5 mol %) and then with a solution of acetophenone (3 mmol) in the corresponding solvent (2 mL). The tubes were then placed in a parallel hydrogenation apparatus and heated to the corresponding temperature, then pressurised with hydrogen gas at 20 bar and mechanically stirred. After 8 h, the parallel hydrogenation apparatus was cooled to room temperature, depressurized, and each tube analysed by GC (DB-Wax).

Under these conditions several solvent with complexes Fe(L-1)(CO)(H)(OC(O)R) were tested. The results are reported in Table 7.

TABLE 7 Hydrogenation of acetophenone using isolated complexes Fe(L-1)(CO)(H)(OC(O)R) with different solvents T Test Complexes C (° C.) Solvent Conv. ROH 1 C1 5000 50 Ethanol 42 42 2 C1 5000 50 Isopropanol 97 97 3 C1 5000 50 Tetrahydrofuran >99 >99 4 C1 5000 50 Heptane >99 >99 5 C1 5000 50 Toluene >99 >99 6 C1 2500 50 Toluene 57 57 7 C2 5000 100 Ethanol 35 35 8 C2 5000 100 Isopropanol 56 56 9 C2 5000 100 Tetrahydrofuran 89 89 10 C2 5000 100 Heptane 47 47 11 C2 5000 100 Toluene 48 48 C: Catalyst ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of acetophenone to the corresponding 1-phenyl ethanol after 8 h. Reaction conditions: H₂ gas (20 bar), 50° C. or 100° C., Solvent (1.5M). ROH: amount of 1-phenyl-ethanol in percent in the reaction mixture as analysed by GC

Example 11 Catalytic Hydrogenation of Aldehydes and Ketones with Complex Fe(L-1)(CO)(H)(OC(O)H) (C1)

A typical experimental procedure is as follows:

In the glow box under argon, test tubes were charged successively with Fe(L-1)(CO)(H)(OC(O)H) (0.5 mol %) and with KBF₄ (10 mol %) or without. Then the corresponding ketones or aldehydes (3 mmol) dissolved in THF (2 mL) was added. The tubes were then placed in a parallel hydrogenation apparatus and heated to the corresponding temperature, then pressurised with hydrogen gas at 20 bar and mechanically stirred. After 16 h, the parallel hydrogenation apparatus was cooled to room temperature, depressurized, and each tube analysed by GC (DB-Wax) showing the conversions into the corresponding alcohols.

Under these conditions several aldehydes and ketones as reported in Table 8 were tested. The results are reported in Table 9.

TABLE 8 Structure and names of aldehydes and ketones. Substrate Structure Name  1

Acetophenone  2

Cyclohexanone  3

Cyclohexenone  4

4,4-Dimethylcyclohex- 2-enone  5

2,4,4- Trimethylcyclohexenone  6

6,6-Dimethylcyclohex- 2-enone  7

2-Pentylcyclopent-2-enone  8

(Z)-2-(Pent-2- enyl)cyclopent-2-enone  9

(E)-4-Phenylbut-3- en-2-one 10

4-Phenylbutan-2-one 11

(E)-4-(2,6,6-Trimethyl- cyclohexenyl)but-3- en-2-one 12

6-Methylhept-5-en-2-ol 13

2-Methylpent-2-enal 14

Cinnamaldehyde

TABLE 9 Hydrogenation of different aldehydes and ketones using complex carbonyl hydridoformate bis[2-(di-isopropylphosphino)ethyl] amine iron (II), (Fe(L-1)(CO)(H)(OC(O)H)). T Test Sub. (° C.) C1/MX2 Conv. ROH Sel. 1 1 50 5000/0    >99 >99 — 2 1 50 2500/100000 >99 >99 — 3 2 50 5000/100000 >99 >99 — 4 3 50 5000/100000 >99 95 95:5 5 4 100 5000/100000 >99 96 99:1 6 5 100 5000/100000 98 97 >99 7 6 100 5000/100000 >99 99 — 8 7 80 5000/100000 >99 71  72:28 9 8 80 5000/100000 87.3 72  86:14 10 9 50 5000/100000 98 89 96:4 11 10 100 5000/100000 >99 99 — 12 11 50 5000/100000 44 42 >99 13 12 50 5000/100000 46 46 >99 14 13 50 5000/100000 >99 98 >99 15 14 50 5000/100000 >99 >99 >99 C1/MX2: Catalyst/KBF₄ ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of the corresponding aldehydes or ketones into the corresponding alcohol after 16 hour. Reaction conditions: H₂ gas (20 bar), 50-100° C., THF (1.5M). ROH: amount of alcohol in percent in the reaction mixture as analysed by GC Sel.: Selectivity given as ratio between unsaturated and saturated alcohol as analysed by GC.

Example 12 Catalytic Hydrogenation of Aldehydes and Ketones with Complex Fe(L-1)(CO)(H)(OC(O)Me) (C3)

Following, the typical procedure as described in Example 11, where complex Fe(L-1)(CO)(H)(OC(O)H) was replaced by complex Fe(L-1)(CO)(H)(OC(O)Me).

Under these conditions several aldehydes and ketones as reported in Table 8 were tested. The results are reported in Table 10.

TABLE 10 Hydrogenation of different aldehydes and ketones using complex carbonyl hydridoacetate bis[2-(di-isopropylphosphino)ethyl] amine iron (II), (Fe(L-1)(CO)(H)(OC(O)Me)). T Test Sub. (° C.) C3/MX2 Conv. ROH Sel. 1 1 100 5000/100000 >99 99 — 2 2 100 5000/100000 >99 >99 — 3 3 100 5000/100000 97 82 99:1 4 4 100 5000/100000 82 81 99.6:0.4 5 9 100 5000/100000 >99 86  88:12 6 11 100 5000/100000 31 20 >99 7 12 100 5000/100000 34 33 >99 8 13 100 5000/100000 >99 91 >99 9 14 100 5000/100000 >99 99 >99 C3/MX2: Catalyst/KBF₄ ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of the corresponding aldehydes or ketones into the corresponding alcohol after 16 hour. Reaction conditions: H₂ gas (20 bar), 50-100° C., THF (1.5M). ROH: amount of alcohol in percent in the reaction mixture as analysed by GC. Sel.: Selectivity given as ratio between unsaturated and saturated alcohol as analysed by GC.

Example 13 Catalytic Hydrogenation of Aldehydes and Ketones with Complex Fe(L-1)(CO)(H)(OC(O)^(t)Bu) (C2)

Following, the typical procedure as described in Example 11, where complex Fe(L-1)(CO)(H)(OC(O)H) was replaced by (Fe(L-1)(CO)(H)OC(O)^(t)Bu)).

Under these conditions several aldehydes and ketones as reported in Table 8 were tested. The results are reported in Table 11.

TABLE 11 Hydrogenation of different aldehydes and ketones using complex carbonyl hydridopivalate bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(H)(OC(O)^(t)Bu)). T Test Sub. (° C.) C2/MX2 Conv. ROH Sel. 1 1 100 5000/100000 89 89 — 2 2 100 5000/100000 >99 >99 — 3 3 100 5000/100000 >99 78 81:19 4 4 100 5000/100000 41 36 >99 5 6 100 5000/100000 40 35 — 6 9 100 5000/100000 >99 86 89:11 7 10 100 5000/100000 29 28 — 8 11 100 5000/100000 48 45 >99 9 12 100 5000/100000 37 35 >99 10 13 100 5000/100000 >99 93 >99 11 14 100 5000/100000 >99 98 >99 C2/MX2: Catalyst/KBF₄ ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of the corresponding aldehydes or ketones into the corresponding alcohol after 16 hour. Reaction conditions: H₂ gas (20 bar), 100° C., THF (1.5M). ROH: amount of alcohol in percent in the reaction mixture as analysed by GC Sel.: Selectivity given as ratio between unsaturated and saturated alcohol as analysed by GC.

Example 14 Comparative Catalytic Hydrogenation of Aldehydes and Ketones with Prior Art Complex (Fe(L-1)(CO)(H)(BH₄) (C5)

Following, the typical procedure as described in Example 11, where complex Fe(L-1)(CO)(H)(OC(O)H) was replaced by complex Fe(L-1)(CO)(H)(BH₄).

Under these conditions several aldehydes and ketones as reported in Table 8 were tested. The results are reported in Table 12.

TABLE 12 Hydrogenation of different aldehydes and ketones using complex carbonyl hydrido borohydride bis[2-(di-isopropylphosphino)ethyl] amine iron (II) (Fe(L-1)(CO)(H)(BH₄) (C5)) compared to complex of the present invention (Fe(L-1)(CO)(H)(OC(O)H) (C1), (Fe(L-1)(CO)(H)(OC(O)Me) (C3) or (Fe(L-1)(CO)(H)(OC(O)^(t)Bu) (C2)). Com- T Test Sub. plex (° C.) C/MX2 Conv. ROH Sel. 1 3 C1 50 5000/100000 >99 95 95:5  2 3 C2 100 5000/100000 97 82 99:1  3 3 C5 50 1000/0    >99 89 89:11 4 8 C1 80 5000/100000 87 72 86:14 5 8 C5 50 5000/0    99 55 57:43 6 9 C1 50 5000/100000 98 89 96:4  7 9 C2 100 5000/100000 >99 86 89:11 8 9 C3 100 5000/100000 >99 86 88:12 9 9 C5 50 5000/0    >99 40 40:60 10 14 C1 50 5000/100000 >99 99 >99 11 14 C2 100 5000/100000 >99 98 >99 12 14 C3 100 5000/100000 >99 99 >99 13 14 C5 50 5000/0    >99 98 98.1:1.9  C/MX2: Catalyst/KBF₄ ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of the corresponding aldehydes or ketones into the corresponding alcohol after 16 hour. Reaction conditions: H₂ gas (20 bar), 50-100° C., THF (1.5M). ROH: amount of alcohol in percent in the reaction mixture as analysed by GC Sel.: Selectivity given as ratio between unsaturated and saturated alcohol as analysed by GC.

Example 15 Comparative Catalytic Hydrogenation of Aldehydes and Ketones with Complexes C1 (Fe(L-1)(CO)(H)(OC(O)H)) and Fe(L-1)(CO)(H)(C1) with MX or Basic Activation Modes

Following, the typical procedure as described in Example 11.

Under these conditions several aldehydes and ketones as reported in Table 8 were tested. The results are reported in Table 13.

TABLE 13 Hydrogenation of different aldehydes and ketones using complexes C1 (Fe(L-1)(CO)(H)(OC(O)H)), and Fe(L-1)(CO)(H)(C1) with MX2 or basic activation modes. Test Sub. Complexes T (° C.) C B MX2 Conv. ROH Sel. 1 1 C1 50 5000 — 100000 >99 95 95:5  2 1 Fe(L-1)(CO)(H)Cl 50 5000 100000 — >99 — Poly. 3 1 Fe(L-1)(CO)(H)Cl 50 5000 — 100000 0.4   0.4 >99 4 4 C1 100 5000 — 100000 >99 96 >99 5 4 Fe(L-1)(CO)(H)Cl 100 5000 100000 — 99 14 25:85 6 8 C1 80 5000 — 100000 >99 71 72:28 7 8 Fe(L-1)(CO)(H)Cl 80 5000 100000 — >99 — Poly. 8 15 C1 50 5000 — 100000 >99 98  0:99 9 15 Fe(L-1)(CO)(H)Cl 50 5000 100000 — >99  4 Poly. C: Catalyst in ppm relative to the substrate. MX2: KBF₄ in ppm relative to the substrate B: Base (tBuOK) in ppm relative to the substrate Conv.: Conversion (in %, analysed by GC) of the corresponding aldehydes or ketones into the corresponding alcohol after 16 hour. Reaction conditions: H₂ gas (20 bar), 50-80° C., THF (1.5M). ROH: amount of alcohol in percent in the reaction mixture as analysed by GC. Sel.: Selectivity given as ratio between unsaturated and saturated alcohol as analysed by GC. Poly.: Polymerisation

Example 16 Catalytic Hydrogenation of Acetophenone Using Complexes Fe(L-1)(CO)(H)(OR) Generated In-Situ

A typical experimental procedure is as follows:

Solutions Stock:

-   -   A solution of complex Fe(L-1)(CO)H 0.015M in THF.     -   A solution of 3M of acetophenone in THF.

In a glow box under argon, test tubes were charged with KBF₄ (10 mol %) or without. Then a solution of Fe(L-1-H)(CO)(H) (1 mL at 0.015M, 0.015 mmol) was added followed by the corresponding alcohol (0.25 ml) and THF (0.75 ml). Finally, acetophenone (1 ml at 3M, 3.0 mmol) was added and the tubes were then placed in a parallel hydrogenation apparatus and heated to the corresponding temperature, then pressurised with hydrogen gas at 20 bar and mechanically stirred. After 1 h, the parallel hydrogenation apparatus was cooled to room temperature, depressurized, and each tube analysed by GC (DB-Wax).

Under these conditions several complexes Fe(L-1)(CO)(H)(OR) as reported in Table 14 were tested. The results are reported in Table 15.

TABLE 14 Structure and names of alcohols used with carbonyl amido bis[2-(di- isopropylphosphino)ethyl] amine iron (II) complex (Fe(L-1-H)(CO)(H)) to generate in situ the complex Fe(L-1)(CO)(H)(OR). Alcohol Structure Name A1

2-Methylbutan-2-ol A2

2-Propanol A3

Ethanol A4 MeOH Methanol

TABLE 15 Hydrogenation of acetophenone using complexes Fe(L-1)(CO)(H)(OR) formed in situ from the corresponding alcohol and the carbonyl amido bis[2-(di-isopropylphosphino)ethyl] amine iron (II), (Fe(L-1-H)(CO)(H)) complex. T Test Alcohol C/A/MX2 (° C.) Time Conv. ROH 1 A1 500/800000/0 100 1 6 6 2 A1 500/800000/100000 100 1 8 8 3 A2 500/1100000/0 100 1 11 11 4 A2 500/1100000/100000 100 1 14 14 5 A3 500/1400000/0 100 1 14 14 6 A3 500/1400000/100000 100 1 40 40 7 A4 500/2100000/0 100 1 15 15 8 A4 500/2100000/100000 100 1 97 97 9 A4 500/2100000/100000 100 8 >99 >99 10  A4  50/2100000/100000 100 24 3 3 11  A4 100/2100000/100000 100 24 45 45 12  A4 200/2100000/100000 100 24 >99 >99 13  A4 500/2100000/100000 50 24 88 88 14  A4 500/2100000/100000 80 24 99 99   15[a] A4 500/2100000/100000 50 24 42 42   16[a] A4 500/2100000/100000 100 24 >99 >99 C/A/MX2: Catalyst/Alcohol/KBF₄ ratio in ppm relative to the substrate. Conv.: Conversion (in %, analysed by GC) of acetophenone to the corresponding 1-phenyl ethanol after the indicated time (h). Reaction conditions: H₂ gas (20 bar), 50° C.-100° C., THF (1M). ROH: amount of 2-phenyl ethanol formed in percent in the reaction mixture as analysed by GC [a]Reactions performed under H₂ gas (5 bar). 

What is claimed is:
 1. A process for the reduction by hydrogenation, using molecular H₂, of a C₃-C₇₀ substrate containing one or two ketone or aldehyde groups into the corresponding alcohol, or diol, wherein the process is carried out in the presence of at least one catalyst in the form of an iron complex of formula [Fe(L3)(L′)(Y)(Z)]  (1) wherein L3 represents a tridentate ligand wherein the coordinating groups consist of one amino or imino group and two phosphino groups; L′ represents a CO or C₁₋₁₁ isonitrile compound; Y represents a hydrogen atom or a C₁-C₁₄ carboxylic radical; Z represents a hydroxyl group, a C₁-C₁₄ carboxylic radical or a linear C₁-C₁₄ alkoxy radical; and optionally a salt of formula MX wherein M is an alkali metal cation and X is a non-coordinating mono anion, wherein the process is performed in the absence of a base.
 2. The process according to claim 1, wherein the ligand L3 is a compound of formula

wherein the dotted line indicates a single or double bond; z is 0 or 1 when the carbon-nitrogen bond with the dotted line represents a double or single bond respectively; R¹ and R², when taken separately, represent, simultaneously or independently, a linear, branched or cyclic C₁ to C₁₀ alkyl or alkenyl group optionally substituted, a C₆ to C₁₀ aromatic group optionally substituted; the groups R¹ and R², when taken together, may form a saturated or unsaturated ring optionally substituted, having 5 to 10 atoms and including the phosphorus atom to which the R¹ and R² groups are bonded; R⁶ and R⁷ represent, simultaneously or independently, a hydrogen atom, a linear, branched or cyclic C₁ to C₆ alkyl or alkenyl group optionally substituted, a C₆-C₁₀ aromatic group optionally substituted; when the dotted line represent a single bond, two R⁶ taken together, may form a saturated heterocycle, optionally substituted and optionally containing one or two additional nitrogen or oxygen atoms, containing 5 to 10 atoms and including the N atom and the carbon atoms to which the R⁶ groups are bonded respectively; and Q represents: a group of formula

wherein n is an integer from 1 to 3, and R⁴ and R⁵ represent, simultaneously or independently, a hydrogen atom, a linear, branched or cyclic C₁ to C₆ alkyl or alkenyl group optionally substituted, a C₆-C₁₀ aromatic group optionally substituted; two distinct R⁴ and/or R⁵ groups, taken together, may form a Cs to Cs, saturated ring optionally substituted, including the carbon atoms to which each of the R⁴ or R⁵ group is bonded; or a diphenyl, dinaphthyl, C₅-C₁₂ metallocediyl, phenylene or naphthylene group optionally substituted; and the optional substituents of R⁴, R⁵, R⁶ and R⁷ are one or two halogen, C₁ to C₁₀ alkoxy groups, halo- or perhalo-hydrocarbon, COOR, NR₂, quaternary amine or R groups, wherein R is a C₁ to C₆ alkyl, or a C₅ to C₁₂ cycloalkyl, aralkyl or aromatic group, the latter being also optionally substituted by one, two or three halogen, sulfonates groups or C₁-C₈ alkyl, alkoxy, amino, nitro, sulfonates, halo- or perhalo-hydrocarbon or ester groups; and the optional substituents of R¹ and R³ and Q, in particular when the groups are or contains phenyl or aromatic groups or moieties, one to three C₁ to C₅ alkoxy groups, C₁ to C₄ alkyl groups, or NR groups, wherein R is a C₁ to C₆ alkyl C₅ to C₆ cycloalkyl.
 3. The process according to claim 1, wherein the ligand L3 is a compound of formula

wherein Q represents: a group of formula

wherein n is an integer from 1 to 3, and R⁴ and R⁵ represent, simultaneously or independently, a hydrogen atom, a linear, branched or cyclic C₁ to C₆ alkyl or alkenyl group optionally substituted, a C₆-C₁₀ aromatic group optionally substituted; two distinct R⁴ and/or R⁵ groups, taken together, may form a Cs to Cs, saturated ring optionally substituted, including the carbon atoms to which each of the R⁴ or R⁵ group is bonded; or a diphenyl, dinaphthyl, C₅-C₁₂ metallocediyl, phenylene or naphthylene group optionally substituted; and the optional substituents of R⁴, R⁵, R⁶ and R⁷ are one or two halogen, C₁ to C₁₀ alkoxy groups, halo- or perhalo-hydrocarbon, COOR, NR₂, quaternary amine or R groups, wherein R is a C₁ to C₆ alkyl, or a C₅ to C₁₂ cycloalkyl, aralkyl or aromatic group, the latter being also optionally substituted by one, two or three halogen, sulfonates groups or C₁-C₈ alkyl, alkoxy, amino, nitro, sulfonates, halo- or perhalo-hydrocarbon or ester groups; and the optional substituents of R¹ and R³ and Q, in particular when the groups are or contains phenyl or aromatic groups or moieties, one to three C₁ to C₅ alkoxy groups, C₁ to C₄ alkyl groups, or NR groups, wherein R is a C₁ to C₆ alkyl Cs to C₆ cycloalkyl.
 4. The process according to claim 1, wherein the substrate is a C₅-C₃₀ compound of formula

wherein R^(a) and R^(b), taken together, represent a C₃-C₂₀, preferably C₄-C₂₀, hydrocarbon group, optionally substituted and optionally comprising one, two or three oxygen or nitrogen atoms; or, when the R^(a) and R^(b) are taken separately, R^(a) represents a hydrogen atom or a R^(b) group; and R^(b) represents a C₁-C₃₀ hydrocarbon group, optionally substituted and optionally comprising one, two or three oxygen or nitrogen atoms.
 5. The process according to claim 4, wherein the substrate is a compound of formula (I) wherein R^(a) represent a hydrogen atom or a R^(b) group, and each R^(b), when taken separately, represent simultaneously or independently a linear, branched or cyclic C₃-C₁₈ aromatic, alkyl, alkenyl or alkanedienyl group optionally substituted; or R^(a) and R^(b) are bonded together and form a C₅-C₂₀ saturated or unsaturated linear, branched, mono-, di- or tri-cyclic group, optionally substituted.
 6. The process according to claim 1, wherein the MX is selected from the group consisted of NaBF₄, KBF₄, or CsBF₄.
 7. The process according to claim 1, wherein Y represents a hydrogen atom.
 8. The process according to claim 1, wherein Z represents a formate, an acetate or a pivalate radical.
 9. The process according to claim 1, wherein Z represents a methoxy radical. 